The Fortran (F77) interface is provided, but certain features have
necessarily been omitted (awaiting Fortran 90). The syntax is
different since there are no pointers in F77. There are no
user-defined types provided in the Fortran interface as Fortran does
not provide structures. Once Fortran 90 has been adopted, user-defined
types will likely appear in the Fortran interface.

Since Fortran does not allow variable argument functions, the
construction of invoices differs from that of the C interface. An
invoice is built up over several function calls, each one specifying
the next field in the invoice.

The above example packs the same invoice that Example 1 does
in C. The last two arguments to ZIP_INV_ADD_INT() and ZIP_INV_ADD_DBLE() are the ``ignore-space'' and ``deferred-sizing''
logicals, respectively, to be explained via examples below. They
also appear in the C syntax, but as part of the argument string via
special characters.